The proposed research focuses on the determinants of the urban mortality transition in the late nineteenth and early twentieth centuries. Although scholars agree that major advances in diet and nutrition, sanitation and environment, and medicine and medical care all contributed to a decline in mortality, few specifics are known about their separate effects. We propose to examine the relative contributions of these various factors through an intensive case study of the shifts in mortality in the city of Philadelphia from 1880 to 1930. Using both published aggregate mortality statistics covering the entire time period, and data for individual decedents from 1880, 1900, and 1930, we will study the changes in the age and cause-of-death structure of mortality during the transition. Our specific aims are threefold. First, to isolate the shifts in cause- and age-specific mortality rates which account for the change in the overall mortality levels in Philadelphia. Second, to examine mortality differentials by race and ethnicity, by geographic area, and by socioeconomic status for the years 1900 and 1930. These efforts will build upon our ongoing analysis of the same differentials in 1880. We will establish whether the mortality decline occurred differentially across population subgroups and across spatial units within the city. Third, to determine the changes in mortality from specific causes in relation to the factors affecting mortality levels. The relative contributions of changes in food and housing, public health measures, and improvements in medical practice along with changes in the population composition and the general environment will be examined for the city as a whole and for small areal units within the city. This analysis will use individual death records in conjunction with data from a combination of sources including vital statistics reports, board of health reports, manufacturing and population censuses, and hospital records.